In accordance with a method described in PCT Application No. WO 2015/120939 A1, when a certain internal pressure is desired in a cavity of a micromechanical component or a gas mixture having a certain chemical composition is to be enclosed in the cavity, the internal pressure or the chemical composition is frequently set during capping of the micromechanical component or during the bonding process between a substrate wafer and a cap wafer. During capping, for example, a cap is joined to a substrate, whereby the cap and the substrate together enclose the cavity. By setting the atmosphere or the pressure and/or the chemical composition of the gas mixture present in the surroundings during capping, it is thus possible to set the certain internal pressure and/or the certain chemical composition in the cavity.
With the aid of the method described in PCT Application No. WO 2015/120939 A1, an internal pressure may be deliberately set in a cavity of a micromechanical component. It is in particular possible with the aid of this method to manufacture a micromechanical component having a first cavity, a first pressure and a first chemical composition being settable in the first cavity, which differ from a second pressure and a second chemical composition at the time of capping.
In the method for deliberately setting an internal pressure in a cavity of a micromechanical component described in PCT Application No. WO 2015/120939 A1, a narrow access channel to the cavity is created in the cap or in the cap wafer, or in the substrate or in the sensor wafer. Subsequently, the cavity is flooded with the desired gas and the desired internal pressure via the access channel. Finally, the area around the access channel is locally heated with the aid of a laser, the substrate material liquefies locally and, upon solidifying, hermetically seals the access channel.
In rotation rate sensors, for example, a very low pressure is enclosed, which is less than 1 mbar, for example. This is the case since, in rotation rate sensors, a portion of the movable structures is resonantly driven. At low pressure, it is very easy to initiate an oscillation with relatively low stresses due to the low damping.
In acceleration sensors, in contrast, it is not desirable that the sensor starts to oscillate, which would be possible if an external acceleration were present. These sensors are therefore operated at a higher internal pressure. The internal pressure of an acceleration sensor is 500 mbar, for example.
A further method for deliberately setting an internal pressure in a cavity of a micromechanical component is described in European Patent No. EP 2 004 542 B1.